Since the articles enter the recesses casually, and since--despite all the devices adopted--it is impossible for all the recesses to be filled with an article, a detecting device is needed to ascertain the presence or the absence of an article in each recess before the latter reaches the wrapping station, whereby, when a recess with no article reaches said station, the supply of a wrapper for the missing article is automatically prevented and a signal is emitted which can be used also for other purposes.
To solve this problem, photo-electrical detectors or radio-detectors are now in general use; these can be used even at a considerable distance from the feeding disc, but are expensive and, above all, are not reliable for long time periods because, due to their use in an environment where dust is likely to be formed, they must be removed periodically for cleaning or even for replacement. The maintenance of such detectors accordingly extremely costly down times due to the discontinued operation of the wrapping machine, which presently reaches very high output rates.